1. Field of the Invention
This invention relates to an ultrasound image processing apparatus and a method of forming and displaying ultrasound images by the apparatus, and in particular relates to an ultrasound image processing apparatus and a method of forming and displaying ultrasound images by the apparatus in which it is possible to produce in a real time base a three-dimensional image which represents an object such as an internal organ of a living body which can not be grasped from the outside thereof.
2. Description of the Background Art
As for image processing apparatuses which utilize ultrasound waves, there are known ultrasound diagnostic apparatuses, fault detectors, fish school detectors and sonar devices and the like. In these image processing apparatuses, ultrasound diagnostic apparatuses are used for diagnosing a living body, in which ultrasound waves are transmitted from a probe toward an object in a living body (e.g. an internal organ or a fetus or the like) and echoes of the ultrasound waves are received by the probe to obtain echo signals, and a tomographic image or the like is produced based on the echo signals to display it on a display or screen such as a CRT or the like.
In the meantime, recently, in the field of such ultrasound diagnostic apparatuses, various techniques have been proposed for obtaining a three-dimensional ultrasound image of an object by transmitting and receiving ultrasound waves to and from a three-dimensional region in which the object such as an internal organ or a fetus is positioned. According to these techniques, there is an advantage that the object can be grasped three-dimensionally or spatially through the three-dimensional ultrasound image.
However, in the prior art techniques, there is a problem that they require a fair amount of computing time for processing an enormous number of coordinate data to form a three-dimensional image. Therefore, it is impossible to obtain such a three-dimensional ultrasound image in a real time base, and therefore these apparatuses can not be practically used. Further, these prior art apparatuses can produce only a three-dimensional surface image of the object, and therefore they are not sufficient for carrying out diagnosis for the internal condition of the object. Such a problem can be seen not only in the ultrasound diagnostic apparatuses for medical use but also in ultrasound image processing apparatuses for use in other field such as sonars and fault detectors and the like.
In view of these problems involved in the prior art apparatuses, the inventors of this application have proposed in its co-pending U.S. application (Ser. No.: 08/682,909) a new ultrasound image processing apparatus which can be preferably used as ultrasound diagnostic apparatuses.
In this ultrasound image processing apparatus, ultrasound beams are emitted from an ultrasound probe toward a three-dimensional region in which an object such as an internal organ of a living body and a fetus or the like is placed while moving the ultrasound probe, and receiving echoes of the ultrasound beams which are reflected from the object. Echo data obtained from the received echoes are sequentially processed to form a three-dimensional ultrasound image (hereinafter, referred to as a "stereoscopic image") of the object in a real time. Further, in this ultrasound image processing apparatus, a new image processing technique which is developed from a volume rendering technique is employed, thereby enabling the apparatus to produce a transparent image of the inside of the internal organ (hereinafter, such a transparent image is referred to as "stereoscopic transparent image") in a real time base.
Therefore, according to the ultrasound image processing apparatus, there are advantages which could not be achieved by the prior art apparatus. Specifically, it is possible to obtain a stereoscopic image (a stereoscopic surface image or a stereoscopic transparent image) of the object in a real time, and it is also possible to grasp the surface condition of the internal organ being examined or the internal tissue structure thereof spatially by observing the stereoscopic surface image or stereoscopic transparent image which is displayed on a screen.
On the other hand, however, in a case where such an ultrasound image processing apparatus is utilized in an actual diagnosis for a living body, there is a case that the internal condition of the organ which is represented stereoscopically can not be grasped accurately. In order to diagnose the inside of such an organ, a tomographic image (B-mode image) is so far used, so that a diagnosing method using such a B-mode image has already been practically established.
Therefore, there is a demand for ultrasound image processing apparatuses which can perform not only an observation of the object through a stereoscopic ultrasound image such as a stereoscopic surface image or a stereoscopic transparent image but also an observation of the object through a B-mode image.
Further, when an internal organ or the like is observed by the ultrasound image processing apparatus, there is a problem that an observation is obstructed by another organ which is positioned in front of or in rear of the organ to be observed, because such other organ is likely to appear in the image displayed in the screen. For example, it is pointed out by doctors that when observing a fetus, a placenta which is positioned at a place closer to the body surface rather than the fetus is likely to appear on the displayed image.